A variety of programmable implantable medical devices are available which typically utilize radio frequency (RF) telemetry for communicating with an external programmer. Such devices include cardiac pacemakers and defibrillators, drug pumps, neuromuscular stimulators, hemodynamic monitors and other physiological monitors. Programming commands or data are transmitted between an implanted RF telemetry antenna and associated circuitry and an external RF telemetry antenna associated with the external programmer. In the past, the external RF telemetry antenna has been contained in a programmer RF head so that it can be located close to the patient's skin overlying the IMD. Programmer RF heads are well known in the art. See for example U.S Pat. No. 4,550,370 issued to Baker, incorporated herein by reference in its entirety. Such telemetry systems may be referred to as “near-field” systems because they require the external antenna to be positioned in close proximity to the implanted antenna in order to establish and maintain telemetry communication.
Long range or far-field telemetry systems have been introduced wherein the external telemetry antenna may be located a distance away from the patient, for example a few meters or so from the patient, during telemetry communication. The external RF telemetry antenna can be located on the case of the programmer or otherwise integrated with the programmer or an associated stand or cart. Such long-range telemetry systems are generally preferable over systems requiring an RF head because it frees the hands of the clinician for performing other tasks during an interrogation or programming session. Moreover, the patient may be active, e.g., performing treadmill or other exercise or stress testing, during a telemetry transmission. Telemetry systems that do not require the use of a programmer RF head are generally disclosed in U.S. Pat. No. 6,240,317 issued to Villaseca et al., U.S. Pat. No. 6,169,925 Villaseca et al., and U.S. Pat. No. 6,482,154 Haubrich et al., all of which patents are incorporated herein by reference in their entirety.
One issue may arise with the use of long-range telemetry systems when the clinician completes a programming procedure and the patient walks away from the programmer but remains within telemetry range of the programmer. An established telemetry session may be maintained between the programmer and the patient's IMD unbeknownst to the patient or clinician. Unintentional programming or interrogation of the IMD may occur as long as the telemetry link is maintained. The clinician may begin a new programming session with a new patient and inadvertently interrogate or program the previous patient's IMD thinking a telemetry link is established with the IMD of the new patient. Another person, unqualified to perform programming operations, may inadvertently program a device that remains within telemetry range of the programmer.
Another disadvantage of an unintentionally sustained telemetry session is unnecessary battery consumption in the IMD. As long as the telemetry link is maintained, the IMD telemetry circuitry will consume battery power in a high-output mode. If the patient remains within the communication range of a programmer after programming and interrogation procedures are completed, IMD battery power is unnecessarily consumed in maintaining the high-output communication link. In past practice, the use of a programming RF head terminated a telemetry link upon removal of the RF head from a position over the implanted device. With the development of long-range telemetry systems, a method is needed for preventing unintentional communication with an IMD and unnecessary IMD battery consumption due to sustained long-range telemetry communication between an IMD and a programmer.